Conveying systems

ABSTRACT

A conveying system for conveying a conveyable material from a hopper where the system includes a fluid port located below the hopper outlet and in a vertical flow path into hopper outlet that can be momentarily opened for an on the go release of a charge of compressed air directly upward into the hopper outlet and into the underside of the bridge in the hopper to either disintegrate or unlock the bridged particles from each other thereby causing the bridged material to fall into the hopper outlet and into the conveying system where the material can be transported to a remote location or to remove any material that may be adhering to the wall during an emptying phase.

CROSS REFERENCE TO RELATED APPLICATIONS

None

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None

REFERENCE TO A MICROFICHE APPENDIX

None

BACKGROUND OF THE INVENTION

This invention relates generally to conveying systems and, morespecifically, to a conveying system and a low energy method ofmaintaining a flow of conveyable material that is subject to bridging.

In conveying solid materials, which may comprise a variety of solidmaterials or particles, the conveyable materials are typically deliveredto a gravity hopper, which contains a cone shaped base that directs theconveyable material to an outlet at the bottom of the gravity feeder.Typically, the outlet connects to a conveying line such as a pneumaticor mechanical conveying line, which conveys the material to a differentlocation. One of the difficulties with delivering conveyable materialsthrough a gravity hopper is that often times the particles of theconveyable materials may adhere to one another and form a selfsupporting bridge over the outlet in the gravity hopper thus preventingflow of the conveyable materials through the hopper outlet. Numerousdevices and methods have been proposed to eliminate the tendency of theconveyable materials to form a material bridge in the hopper or to breakup a bridge of conveyable material in the hopper.

U.S. Pat. No. 3,195,775 shows an example of a device that vibrates ahopper to break a material bridge in a hopper, unfortunately vibrationof the hopper can prematurely decrease the life of the system as well asconsume a large amount of energy.

U.S. patent publication 2003/0017012 shows an air knocker that ismounted on the side of a storage tank with the air knocker having anelastic sheet or diaphragm that attaches to the side of the storage tankfor blasting pulsed air. A permanent magnet holds the valve in a closedstate until the magnetic force is overcome, which enables one to blastair into the side of the storage tank or the bottom of the tank in orderto fluidize the material in the tank. In one embodiment air is blastedpast an elastic member that is mounted on the sidewall of the hopper.

U.S. Pat. Nos. 3,788,527, 4,767,024 and 4,496,076 show the use of airblasters that inject air through the sidewall of a hopper. The airblasters are mounted on a hopper with the air blasters containing arelatively large volume of air under significant pressure and a quickrelease valve for suddenly blasting the volume of air directly into theconveyable material. U.S. Pat. No. 4,496,076 shows examples of airblasters mounted to cone of the hopper and with the air blastersdirecting a blast of air downward or tangentially with respect to thewall of the hopper in order to break up a bridge of conveyable material.This type of device requires a large amount of energy to break up thebridge and has been referred to as the creation of a “dull explosion” inthe material.

U.S. Pat. No. 6,007,234 shows a fluid injector that directs air along asurface wall of the hopper to dislodge materials located along thesidewalls of the hopper. This type of device minimizes bridging byinhibiting materials from adhering to the sidewall of the hopper. Inthis type of apparatus multiple fluid injectors may be mounted in thehopper sidewall to keep material from adhering to the sidewall of thehopper and thus inhibiting bridging.

U.S. Pat. No. 4,826,051 disclose another high energy manifold blasterthat attaches to the side of the hopper to pulverize the particulatematter in the hopper so the material can flow through the hopper.Generally, multiple units are mounted in the hopper sidewall.

As can be seen from the above prior art it is difficult to continuouslyconvey bridgeable materials due to the problem of bridging of conveyablematerials, which has given rise to numerous methods and apparatus. Somemethods employ brute force by shaking the bin or blasting air through asidewall of the hopper and into the side of the bridged material tobreak up a bridge while other methods and apparatuses attempt to preventa bridge of conveyable material from forming in the hopper by directingair along a sidewall of the hopper through a plurality of openings inthe sidewall. Compounding the problem of conveyable materials, which maybridge, is that some bridges within the hopper may be broken easilywhile others are extremely difficult to break up.

The prior methods have certain disadvantages in that some methods maysubstantially increase noise level proximate the hopper, some mayshorten the life of the system, some may require large amounts of energyor some require multiple air blasters or bin aerators mounted to thesides of the hopper, which increases both the complexity and costs ofthe system. In some cases the prior art methods are simply ineffectiveand instead of dislodging bridged material an air blaster may form a“rat hole” in the bridged material, which is a passageway from theblaster to the hopper outlet that does not break up the bridge butprevents the bridged material from falling into the hopper outlet.

SUMMARY OF THE INVENTION

A conveying system for smoothly and continually conveying materials fromone location to another where the conveyable materials have a tendencyto self adhere and form a material bridge of conveyable materials whichblocks the flow of conveyable materials through the conveying system.The conveying system includes a source of air that can on the go beintermittingly released into the underside of a bridge of conveyablematerial to disintegrate the bridge of a conveyable material over ahopper outlet. By directing a pulse or charge of air into an undersideof a bridge of normally conveyable material in a gravity hopper in adirection that is opposite to the normal gravitational flow of theconveyable material through the hopper outlet it has been found that onecan maintain a continuous flow of conveyable material through thesystem. In one example an outlet fluid port for the source of air islocated below the hopper outlet and in a vertical flow path of materialfrom the hopper outlet with the upward facing fluid port momentarilyopening to release a charge or pulse of compressed air directly upwardinto the hopper outlet. The charge or pulse of air flows upward into andthrough the hopper outlet and into the underside of bridged particles inthe hopper, where the charge of air dissipates into the bridgedmaterial, which disintegrates or unlocks the bridged particles from eachother causing the bridged material to collapse and fall into the hopperoutlet. After release of the charge of air the fluid port closes, whichallows the bridged material to fall downward through the hopper outletand into a conveying system where the material can be transported to aremote location. Since the bridge is quickly broken with a charge orpulse of air from beneath the bridged material no devices need to bemounted to the sidewalls of the hopper and the energy use in breakingthe bridge is minimized since a single release of a charge of air intothe bottom outlet of the hopper can break up the bridged material in thehopper. Thus, one can maintain a flow of materials through the conveyingsystem since bridged material in the hopper can be quickly broken on thego with an air jet or a release of a pulse of air into the underside ofthe bridge. In the event a further bridge may form one can repeat theprocess as needed to keep the material flowing through the hopper outletby continually supplying pulses or charges of air to the hopper inlet,which may be pulses of air.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a gravity hopper for delivery ofconveyable material to a conveying system and a bridge breaker;

FIG. 2 is a cross sectional view of the conveying system and bridgebreaker in the closed condition;

FIG. 3 is a cross sectional view of the conveying system and bridgebreaker in the open condition;

FIG. 4 is a cross sectional view of the conveying system and bridgebreaker in the open condition with a butterfly valve located at theinlet; and

FIG. 5 is a cross sectional view of the conveying system and bridgebreaker in the open condition with a set of bin aerators mounted on thecone wall of the hopper.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a cylindrical gravity hopper 10 having a vertical axis 9extending through a cylindrical hopper inlet 11 located at the top ofthe hopper and a cylindrical downward facing or downward discharginghopper outlet 12 located at the bottom of the hopper. Hopper 10 includesa domed top 15 with a port 13, a port 14 and hopper inlet 11 locatedtherein. In this example hopper 10 includes a cylindrical sidewall 15 aand an intermediate open-ended cone 15 b that converges from cylindricalsidewall 15 a to a cylindrical hopper outlet 12, which has a cylindricalvertical sidewall 12 a for directing material away from and out of thehopper 10. A flange 15 c on outlet 12 allows one to secure a conveyingsystem 30 to hopper outlet 12. Typically, one directs a batch ofconveyable material into the hopper inlet 11 of the gravity hopper 10where the conveyable material is gravitationally funneled to the hopperoutlet 12 located at the bottom of the hopper 10. The conveyablematerial discharging from the hopper outlet is then transported to adifferent location through a conveying system 30, which for example maybe a pneumatic conveying system or the like.

A reference to FIG. 1 shows hopper 10 contains a conveyable material 20,which is in contact with the interior surface of frusto conical sidewall15 d with conveyable material 20 forming a self-supporting bridge overthe hopper outlet 12 with the bridge having a top surface 20 b and anunderside 20 a. The formation of the bridge through the self-adhesion ofconveying material particles to one another prevents normally conveyablematerial 20 from falling into the pneumatic conveying system 30, whichis located below the outlet 20. In this example the pressure P₁ on topof the conveyable material is insufficient to force the material 20through the outlet 12 and increasing the pressure P₁ may further compactthe bridged material 20 without breaking the bridge. Typically, thebridge of conveyable material 20 has the highest bulk density at thebottom of the bridge than at the top of the bridge since the pressurefrom the weight of the conveyable material increases the density of theconveyable material, which strengthens the bottom of the bridge, thusrequiring large amounts of energy to break up the bridge if one blastsair laterally or downwardly into the bridged material.

A circular flange 32 a on conveying housing 32 connects to a circularflange 15 c on hopper outlet 12 through bolts or the like to hold theconveying housing 30 proximate the hopper outlet 12. An air inlet 31connects to one side of housing 32 for supplying conveying air to aconveying pipe 33, which extends from the opposite side of the housing32. In normal operation the conveyable material 20 falls downwardthrough the hopper outlet 12 and into the conveying housing 32 where theincoming air from air inlet 31 and conveying pipe 33 fluidly transportthe conveyable material to another location. In general the conveyablematerial 20 is transported from the gravity hopper 14 to a remotelocation through the conveying line 33 as long as the conveyablematerial remains in a fluidized or flowable state within the hopper.However, from time to time conditions occur in the hopper that cause thenormally conveyable material 20 to form a bridge of over the hopperoutlet, which stops the flow of conveyable material through the hopperoutlet 12. Still in other cases some materials may form bridges sofrequently that one simply foregoes the use of a gravity hopper forconveying the materials. FIG. 1 illustrates a typical static bridge ofconveyable material 20, which has a top surface 20 b and a bottom orunderside 20 a that has been formed into a solid bridge that extendsfrom side to side of the hopper thus preventing the conveyable material20 in hopper 10 from falling into the hopper outlet 12.

As shown in FIG. 1 and FIG. 2 the conveying system 10 includes a gravityhopper 10 having a hopper outlet 12 for gravitationally directing aconveyable material 20 downward into the hopper outlet 12 where it isreceived in a conveying chamber 35 which can carry the material to afurther location. Located directly below the hopper outlet 12 is anupward facing fluid port 39 for on the go directing of a pulse of airvertically upward into and through the downward facing hopper outlet 12and into an underside of a bridge of conveyable material 20, which islocated over the hopper outlet 12. The release of a short pulse or asmall charge of air upward into the hopper outlet and into the undersideof the bridge causes a disintegration of the bridge of conveyablematerial that starts from below the bridge of conveyable material andthus requires a minimum of energy as opposed to high energy methods ofblasting air into the top or side of the bridged material, which in somecases may not even break up the bridge but form “rat holes” through thematerial.

FIG. 2 is an isolated view of a conveyer 30 and one example of a bridgebreaker 40 sharing a common vertical, cylindrical, sidewall 32, whichincludes a top flange 32 a for attachment to a flange 15 c on the bottomof hopper outlet 12 through bolts or the like. In this example housingsidewall 32 forms a common vertical sidewall for both the conveyer 30and bridge breaker 40 although if desired the bridge breaker may beseparate from the conveyor system 30 or may be used without a conveyorsystem. In this example a disk member or separator 41, which is securedto inner cylindrical sidewall 32, separates the conveyor system 30 fromthe bridge breaker 40 with the disk 41 having a fluid port 39 that canbe opened or closed in response a need to break up a bridge or prevent abridge from forming in the hopper 10.

FIG. 2 shows bridge breaker 40 in a closed condition where a materialreceiving chamber or conveying chamber 35 in the conveyor 30 is isolatedfrom a bridge breaker air chamber 50 in the bridge breaker 40. In thisexample, bridge breaker 40 includes a slideable piston or retractableplug 43 having a central shaft 43 c, a first end 43 a in engagement withthe retractable plug including a rigid collar 45 that engages acompression spring 46 and a second end 43 e with piston 43 having a topface 43 d and a bottom face 43 b. A slideable seal 43 f extends aroundthe periphery of the second end 43 e to form a seal between the chamber53 above the top face 43 d and the chamber 53 below the bottom face 43b. Annular seal 49 and annular seal 47 permit axial sliding of centralshaft 43 c, while annular seal 48 forms a seal between base 52 and basecollar 51. In this embodiment the compression spring 46 engages theretractable plug 43 for quickly urging the retractable plug into aclosed condition after a portion of the air in the air chamber has beenreleased through the fluid outlet port 39.

A resilient cap 44 on the top end of piston 43 includes acircumferential lip 44 a that extends over collar 45 with a top face 44b forming sealing engagement with the underside 42 b of collar 42 toprevent air flow therethrough when in the closed condition. That is, theaxial pressure generated by compression spring on piston 43 maintainsfluid port 39 in a normally closed condition in the absence of a controlpressure from control station 60 as compression spring 46 biases piston43 toward a closed condition that sealingly closes the top fluid port 39to prevent a conveyable material from falling into the chamber 50. Insome instance rapidly closing the fluid port 39 can be used to preventfluid from falling into the fluid port or one may maintain a flow of airthrough the top fluid port sufficient to deflect conveyable materialaway from the fluid port without actually blocking the fluid port 39 orinterfering with the material falling into chamber 35. As describedherein control station 60 can open and close the air outlet or fluidport 39 to deliver either a pulse of air, a series of pulses of air or acontinual flow of air into the hopper outlet.

Collar 42 includes a central passage or fluid port 39 formed by sidewall42 a, which connects to the conveyor air chamber 35 in conveyor 30. Inthe closed condition shown in FIG. 2 the lower air chamber 50 in bridgebreaker 40, is isolated from the top conveying air chamber 35 byresilient cap 44, which prevents flow therebetween.

FIG. 2 shows bridge breaker 40 includes an air chamber 50, which issupplied with pressurized air through an air inlet 59. Located withinthe base of chamber 50 is a base collar 52 having a verticaldisplaceable piston 43 therein. In operation chamber 50 receives andstores a pressurized gas from air inlet 59 with the source ofpressurized air having a stagnation air pressure greater than an airpressure in the hopper outlet 12 so that a release of air from chamber50 can be directed upward through the chamber 35 and into the hopperoutlet 12 during the operation of the conveying system.

Cylindrical housing 32 includes a top member 41 having a top fluid port39 that opens vertically upward into the hopper fluid outlet 12 as thefluid port 38 is positioned directly below the gravity hopper flowoutlet 12 with the top fluid port 39 shown positioned in a vertical flowpath of material discharging from hopper 10 as indicated by a verticalaxis 9. Piston 43 is axially and vertically slideable with piston 43having a top end 44 movable from a closed condition, which is shown inFIG. 2, where the top fluid port 39 is in a closed condition to preventflow therethrough to an open condition, which is shown in FIG. 3, wherethe top fluid port 39 is in an open condition so that a charge ofpressurized air released from the chamber 50 flows upward through thetop fluid port 39, the hopper outlet port 12 and into the bridgeunderside 20 a to thereby disrupt and disintegrate the bridge, whichallows the material 20 forming the bridge to fall downward through thehopper outlet 12 and into the material conveying chamber 35 where it canbe transported to a different location by the conveying member 30.

In this example a control station 60 connects to a top portion of apiston chamber 53 through a first conduit 62 that supplies a controlfluid such as air to a topside 43 d of piston 43 in piston chamber 53.Similarly, control station 60 has a second conduit 61 that connects to abottom portion of piston chamber 53. Control station 60 may be manuallyoperated or may be automatically operated to supply the control fluidneeded to slide piston 43 up or down to open or close the port 39between conveying system 30 chamber 30 and bridge breaker air chamber50.

Upon detection of a bridge in hopper 10 a signal is sent from controlstation 60 to slide piston 43 downward, which opens the fluid port 39and automatically releases a charge of air from air chamber 50 into thehopper outlet 12, where the charge of air flows upward into the bridgebottom 20 a to break up the bridged material in the hopper 10. Afterrelease of the charge of pressurized air a further signal is sent toslide the piston 43 upward to close the outlet port 39 so the bridgedmaterial can fall into the hopper outlet 12 and be delivered to theconveying system 30 rather than falling into port 39. In addition theforce of compression spring 46 may be set such that it closes port 30when the charge of air escaping from the air chamber is reduced in airchamber 50. As can be seen the invention comprises a bridge breaker fora gravity hopper having a downward facing hopper outlet and a source ofair with the source of air having an upward facing outlet in alignmentwith the downward facing hopper outlet for directing a charge of airfrom the source of air vertically upward into the hopper outlet todisrupt or prevent blockage of flow of a conveyable material through thehopper outlet.

A feature of the invention is that the delivery of a charge of air onthe go, which is directed vertically upward into the hopper outlet 12and into the underside 20 a of a material bridge, requires less energyto break up a bridge in the hopper then conventional blasters or binvibrators. The air pressure P₂ in the chamber 50 for breaking the bridgemay be equal or less than the air pressure P₁ on top of the bridge asthe bridged material forms an air seal between the top and bottom of thehopper. FIG. 1 shows that the pressure P₁ above the bridge is notgenerating sufficient force to push the bridged material into the outlet12. However, the release of a small charge of air from air chamber 50,where the stagnation pressure P₂ may be equal or even less than thepressure P₁, is sufficient to break up the bridged material throughengagement with the bridge underside 20 a. For example, it has beenfound that momentarily releasing a charge of air, from air chamber 50,which is at stagnation pressure P₂ which is equal or less the pressureP₁, into the hopper outlet 12 and the underside of the bridge dislodgesor loosens the bridge particles at the bottom of the bridge, whichcauses the bridge to collapse allowing the conveyable material 20 in thehopper to flow through the hopper outlet 12. Thus, in the inventiondescribed herein the air does not need to be blasted into the bridgedmaterial in order to force the particles into the hopper outlet. Thatis, where the prior art forces the particles laterally or toward thehopper outlet the present invention momentarily directs a charge of airupward into the hopper outlet and into the underside 20 a of the bridge,which causes the bridged particles to disintegrate and fall downwardinto the hopper outlet 12. The momentary on the go delivery of a chargeor pulse of air to dislodge the bridged material from beneath the bridgecan be done quickly, quietly and efficiently with minimum energyconsumption so that the conveying can continue without interruption.

In the example shown a flow sensor 70, which is located in the conveyorsidewall 32 can be used to detect the presence of flow into theconveyor. For example flow sensor may be a conventional optical sensor,which senses the presence or absence of materials flowing through theconveying system. If no flow is detected in conveying chamber 35 controlstation 60 receives a no flow condition and automatically sends a signalto retract piston 43, which causes the cap 44 to move downward andunblock port 39 thus releasing a charge of air from chamber 50, whichflows upward into the bridge underside 20 a. The contact of the pulse orcharge of air with the underside of bridged material quickly breaks thebridged material, which allows the bridged material to flow into theconveying chamber 35. Conversely, if the flow sensor 70 determines thatthe conveyable material is flowing control station 60 maintains thepiston or retractable plug 43 in the closed condition as shown in FIG.2.

In this example the conveying system includes a housing 32 having anintegral air chamber 50 for holding air at a stagnation pressure, whichis in excess of an air pressure P_(x) on the underside of the bridge ofconveyable material. A fluid port 39 in the housing releases a portionof air from the air chamber 50 into the hopper outlet 12 withoutallowing a dynamic air pressure P_(x) in the conveying chamber 35 andthe air pressure in the chamber 50 to equalize, which could prevent flowthrough the conveyor. However, other methods of releasing a charge ofair may be used without departing from the spirit and scope of theinvention.

As described herein the invention includes an on the go method formaintaining the flow of conveyable material through a gravitationalhopper 30 with the method of conveying material from a gravity hopper 10comprising the steps of directing a conveying material 20 into a gravityhopper 10, gravitationally directing the conveying material downwardinto a hopper outlet 12, conveying the material 20 away from the hopperoutlet 12 and directing a pulse of air upward into the hopper outlet 12in the event the conveyable material stops flowing through the hopper10.

A feature of the method is that even though the pulse or charge of airis directed vertically upward into a bridged region of the conveyablematerial where a bulk density of the conveyable material is highest thebridged material can be quickly broken to allow material to flow throughthe hopper outlet. Depending on the pressures in some instances thepulse of air may travel as a shock wave into the hopper outlet 12.

During the conveying of material in the conveying system of theinvention described herein one normally maintains an air pressure on atopside of conveyable material P₁ at proximately the same as an airpressure P_(x) on the underside of the conveyable material through aperiodic directing of the pulse of air upward into the hopper outlet 12and opposite to a gravitational flow direction of the conveyablematerial from the hopper outlet 12. That is, instead of delivering asingle pulse of air to the hopper inlet one may continually cycle theair on and off to provide for timed pulses of air into the hopperoutlet. One method of providing air for directing into the hopper outletis to maintain a source or air in a chamber 50 where a stagnationpressure of the air in a chamber 50, which connects to the hopper outlet12, is maintained at a pressure greater than the air pressure P_(x) inthe hopper outlet.

In this method one preferably directs the pulse or charge of air fromchamber 50 vertically upward into the hopper outlet 12 while there is nodownward flow of conveyable material through the fluid outlet 12.Typically, the pulse of air released from an air chamber, which has astagnation pressure greater than an air pressure in a conveying outletconnected to the fluid outlet, quickly flow into and through theconveying chamber 35 and into the hopper outlet. That is, a pulse orcharge of air released into the hopper outlet 12 flows upward directlyinto particles on an underside 20 a of the bridged region of conveyablematerial 12 in the hopper 10, which breaks up the bridge on the go.

During the conveyance of materials 20, which may either dry or wet, theconveyable material begins to consolidate and compact as the materialsenter the gravity hopper 10 resulting in the bulk density of theconveyable material being at its highest near the hopper outlet 12,which is located at the bottom of the hopper 10. In addition, the longerthe material 20 sits in the gravity hopper 10 the more the materialconsolidates and compacts in the hopper, which increases the difficultyin dislodging the material 20 from the hopper 10.

Increasing the downward forces on the material 20 at the top of thehopper 10 either by adding more material or increasing the air pressureP₂ may be counter productive as the increased pressure squeezes orcompacts the material, which makes it more difficult for the conveyablematerial to flow out of the hopper under the force of gravity. Theconsolidation or compaction of material 20 at the lower cone sectionabove the hopper outlet 12 is a major problem to gravity feeding of mostmaterials as the material may squeeze together and compact into anunflowable condition in response to upstream pressure on the materials20.

The material at the top of hopper 10 has the lowest bulk density and asmaterial 20 is added to the top of the hopper 10 it increases the weighton the material at the bottom of the hopper, which in some casessqueezes the material at the bottom of the hopper to the point of beingrock hard and resistant to gravity flow. Consequently, The material atthe bottom of the hopper, which is compacted together, has a much higherbulk density that any material located above the bottom of the hopper.As a result it has been found it becomes more difficult if notimpossible to dislodge and gravity feed materials through the hopperoutlet at the bottom of the hopper if the materials forms a bridge overthe hopper outlet. Consequently, the lodging or bridging of material inthe cone of the hopper 10 may become so compacted that even devices thatblast air through ports in the side of the cone wall 15 b may fail todislodge the material from the hopper 10. Likewise increasing airpressure P₂ at the top of the hopper in order to force the materialthrough the hopper outlet 12 has the effect of squeezing or compactingthe material in the lower cone of the hopper 10 thus making it moredifficult to convey materials through the hopper.

A feature of the invention described herein is that materials, which arenormally extremely difficult or may be impossible to gravity feed, canbe conveyed through and from the hopper 10.

FIG. 4 shows a cross sectional view of hopper 10 with an inlet 12 and abutterfly valve 80 for opening and closing the pressurized inlet pipe81. The system of FIG. 4 is identical to the system shown in FIG. 1except a butterfly valve 80 is used to open and close the supply pipe 82to the hopper 10. Suitable butterfly valve are shown and described inapplicant's U.S. Pat. Nos. 4,836,499; 5,295,659 and 8,256,448 and arehereby incorporated by reference. In this example the conveyablematerial 20 under pressure flows through pipe 81, butterfly valve 80 andinlet 82 and then flows downward as identified by 20 d onto the materialtop 20 b of material 20. Located below the hopper outlet 12 is thebridge breaker 40 that contains a charge of air for directing upwardinto the outlet and into the underside of the bridge where some of theair may flow upward along the sides of the hopper 10. While a butterflyvalve is shown a ball valve or any other type of valve may be used sothat the hopper can be pressurized to normally push or convey materialthrough the hopper and to its intended destination.

FIG. 5 shows a system identical to the hopper 10 in FIG. 1 and FIG. 4except in this application a set of fluid injector or bin aerators 85and 86 are located on the cone wall 15 b to provide an option fordislodging or aerating materials in the hopper. Bin aerators 85 and 86may be used independent or in conjunction with bridge breaker 40depending on the material being conveyed. An example of a bin aerator isshown in applicants U.S. Pat. No. 3,952,956, which is herebyincorporated by reference. In the example shown in FIG. 5 compressed airis supplied to cone sidewall though air pipe 86 a and bin aerator 86 aswell as through air pipe 85 a and bin aerator 85.

A further feature of the invention described herein is that the bridgebreaker 40, which operates through the hopper outlet 10, is compatiblewith existing systems. That is, directing a charge of compressed airupward into the bridged material in the hopper 10 to dislodge bridgedmaterial from below so the material can feed out of the hopper outlet 12may be incorporated into existing conveying systems even if otherdevices are maintained on the hopper since the bridge breaker can bemaintained outside the hopper and can operate independently of theoperation of other devices attached to the hopper 10.

Another feature of invention of directing a charge of compressed airupward though the hopper outlet 12 is the sidewall cleaning benefitobtained during the emptying of the hopper when there may be no bridgingin the hopper. Normally, as the material empties out of the gravityhopper 10 some material may adhere to the sidewall of the hopper. Withthe present invention one can quickly remove any residue material thatmay be adhering the hopper walls as the charge of air entering throughthe hopper outlet 12 travels upward through the hopper 10 where itsweeps along the conical hopper walls 15 b, which loosens any remainingmaterial that may be adhered to the walls thereto thereby enabling acomplete emptying of the hopper.

The conveying system has been described herein with a single release ofa charge a pulse of air or a continually release of charges or pulses ofair that are directed upward into the hopper outlet, however, as analternate embodiment a continuous upward stream of air or an air jet,which is either a variable velocity stream of air or a constant velocitystream of air, may be introduced into the bottom of the hopper outlet tomaintain difficult materials in a flowable condition. In the continuousflow application the upward flowing air jet may be sufficiently small soas not to block the downward flow of conveyable material into the hopperoutlet but sufficiently large to maintain the material in the hopperoutlet in a fluidized condition by breaking or preventing bridges fromforming in the hopper outlet. In this application either the momentum ofthe falling conveyable material in the hopper can be used to overcomethe upward force of the continuous jet or the continuous flow jet mayhave a smaller diameter than the hopper outlet so that both an upwardflow of air into the hopper and a downward flow of material from thehopper can coexist in the same passage.

While the system has been described as to use of air no limitation isintended thereto as the air may be a single gas or various combinationsof gases, which are suitable for the conveying of bridgeable materials.

I claim:
 1. A conveying system comprising: a gravity hopper having a top opening for receiving a conveyable material and a lower hopper outlet for directing the conveyable material therefrom wherein the conveyable material is subject to forming a bridge over the lower hopper outlet thereby preventing flow of the conveyable material from the gravity hopper; a housing having a material receiving chamber connected to the hopper outlet for carrying the conveyable material away from the lower hopper outlet; a bridge breaker located vertically below the lower hopper outlet with said bridge breaker having a fluid chamber therein and a top fluid port located in a separator between the material receiving chamber and the fluid chamber in the bridge breaker, said bridge breaker including a slideable piston having a first end momentarily displaceable for opening or closing the top fluid port in the separator; and a source of pressurized gas located in the fluid chamber for an on demand delivery of a charge of gas upward through the top fluid port when the top fluid port is in an open condition with the charge of gas flowing upward into an underside of a bridge of material over the hopper outlet to disintegrate the bridge of material from below thereby allowing the conveyable material forming the bridge to fall into the material receiving chamber in the conveying system.
 2. The conveying system of claim 1 wherein the piston comprises a shaft with the first end including a resilient cap for blocking the fluid port when the piston is in a closed condition and a second end larger than the first end with the second end located in a further chamber with the second end having a top face and a bottom face isolated from each other through a slideable seal, said piston responsive to a differential pressure between the top face and the bottom face of the second end for axially displacing the piston from a closed condition to an open condition or from an open condition to a closed condition through changing the differential pressure on opposite faces of the second end.
 3. The conveying system of claim 1 wherein the gravity hopper has a central axis and the top fluid port is located along the central axis.
 4. The conveying system of claim 1 including a control station for manually opening and closing the top fluid port in response to a flow condition in the gravity hopper.
 5. The conveying system of claim 1 including a sensor for detecting the presence of a bridge in the hopper with the sensor connected to a control station to momentarily open the top fluid port either automatically or through an operator activation.
 6. The conveying system of claim 1 wherein a stagnation pressure in the bridge breaker P₂ is less than the pressure P₁ above the bridge and the charge of gas comprise a continuous flowing air jet, a variable flowing air jet, a single pulse of air or a repeated pulse of air.
 7. The conveying system of claim 1 wherein the piston includes a compression spring for normally maintaining the piston in a closed condition in the absence of a control signal from the control station.
 8. The conveying system of claim 1 including a retractable plug for opening and closing the fluid outlet port in response to formation of the bridge of conveyable material over the hopper outlet.
 9. The conveying system of claim 1 including a pneumatic conveying line connected to the hopper outlet with a source of conveying air connected to the conveying line. 